Resourceful utilization of quarry tailings in the preparation of non-sintered high-strength lightweight aggregates

Abstract

Quarry tailings are usually stockpiled due to stable crystalline structures below 100 °C and abundant sources, which lead to a serious environmental impacts and high ecological risks. This paper presents a study of transforming the fly ash and quarry tailings as the main raw materials into lightweight aggregates (LWAs) for using in civil engineering. A novel curing regime (autoclave technology) has been proposed to obtain higher compressive strength of LWAs. The effects of curing parameters (including temperature and steam pressure) on the properties (compressive strength, water absorption, loose bulk density, phase composition, pore structure and microstructure) of LWAs were systematically evaluated. On the other hand, this research also studies the effect of cement content on the basic properties of LWAs, which was decreased from 30 to 10 wt% for declining the CO2 emission. Results show that the strength sharply increases from 2.48 to 11.95 MPa and the water absorption decreases from 11.2 to 2.09% with increasing the elevated curing temperature from 25 to 190 °C. The LWA prepared with 70 wt% solid wastes (fly ash and quarry tailings) at 190 °C achieved the highest strength (11.95 MPa) and the lower loose bulk density (1160 kg/m3), which could meet the requirement of Chinese LWAs standard (GB/T 17431.1-2010). The water absorption of LWAs is below 5% except sample T25. The total porosity of LWAs decreases from 39.65% to 26.32% at 150 °C and from 42.54% to 27.24% at 190 °C while the cement content increases form 10 wt% to 30 wt%. At the same time, the percentage of pores (>50 nm) also gradually decreases. While the curing temperature, pressure and cement usage are above 150 °C, 1.00 MPa and 10 wt% respectively, will promote the formation of new phase composition (analcime). That also further increases the strength and percentage of harmless pores and few harmful pores. Therefore, this research offers a new curing method for producing LWAs from 70 to 90 wt% solid waste and is a rapid and sustainable solution for the large-scale recycling of quarry tailings.